This invention relates to a longitudinally movable chuck with a motorized drive for winding cores.
Conventionally, chucks grip a winding core at both ends or grip both ends of a set of winding cores arranged in line in a roll bed of a winding machine. For this purpose, the chucks are run into the core ends by a motor. Apart from their exact axial positioning, the cores require an axial tensioning by a clamping force of a well-defined magnitude. To achieve this clamping force, the electric motor drive is used for axial adjustment of a chuck. A motor control system records the speed drop of the motor which occurs after the chuck stop grips the end face of the core, this drop being due to the adjustment resistance, and switches the motor off. Because of this mode of operation, the clamping force is subject to considerable fluctuations during successive clamping operations and is especially strongly influenced by frictional resistances in the drive line of a chuck.
From DE-Patent Specification No. 28 15 310, a chuck of the aforementioned type arranged at the end of a longitudinally movable shaft is known, which discloses axially shiftable internal wedge pieces mounted on a shaft end. This arrangement is fitted with external wedge pieces likewise guided to be axially movable on the internal wedge pieces. Upon introduction of the chuck into a winding core, the core which grips with its end face a stop of the external wedge pieces causes an axial shifting of these wedge pieces relative to the internal wedge pieces. The external wedge pieces spread out until they come to rest at the core inside periphery. The continued axial movement of the chuck now results in a simultaneous shifting of the external and internal wedge pieces relative to the shaft end against the force of a compression spring which is located in the shaft end as well as supporting itself on the one side against the shaft and on the other side directly against the internal wedge pieces.
The spring clamping force reaches its maximum value when the external and internal wedge pieces run onto a stop of the chuck shaft. This force which acts axially against the winding core can be influenced by changing the preloading of the compression spring, but it varies in its magnitude because of the tolerances of the core inside diameter, which alter the shifting path of the external wedge pieces relative to the internal wedge pieces, and thus the deflection of the compression spring. In addition, the winding core is loaded by axial forces of different magnitudes because of the tolerances in the shut-down time point of the axial drive moving the chuck, since the external wedge pieces have run against the stop of the chuck shaft. The strongly differing axial forces acting on a winding core or a set of cores clamped between two chucks are partly absorbed by the elastic deformation of the cores which are made of board, and partly by the support of the chuck as well as its guide carriage in the machine frame of the winding machine. Excessive axial forces, however, may cause damage to the thrust bearings, after a relatively short operating time of the winding machine, especially if steel winding cores are used instead of board winding cores.
An object of the invention is therefore to create a chuck whose axial clamping force acting on a winding core is adjustable to a relatively precise extent.